This invention relates to a substrate with components mounted thereon which has been completed or is still in its production process and more particularly to a method and a system for carrying out inspections by using X-ray transmission images thereon. The invention also relates to a method of producing such a component mounting substrate while carrying out such inspections in each of production processes that are carried out sequentially.
The general production process for component mounting substrates includes a solder printing process in which a printed circuit board is printed upon with cream solder, a component mounting process in which components are placed at positions where cream solder has been applied and a soldering process in which the substrate loaded with the components is heated for soldering. Along a production line for carrying out these processes sequentially, it is a common practice to carry out an inspection after each process such that substrates with a defect generated in that process will not be delivered to the next process.
It has been known to use an X-ray transmission image for an inspection of this type. Japanese Patent Publication Tokkai 6-237076, for example, disclosed an inspection apparatus for inspecting the soldered condition of a substrate by using an X-ray transmission image. Japanese Patent Publication Tokkai 2001-50730 relates to the production of a substrate with components mounted to both of its surfaces by obtaining a differential image showing the difference between its X-ray transmission image obtained when the mounting of components onto its one side has been completed and the image obtained after the mounting of components onto both sides has been completed and inspecting the solder condition on the second substrate surface.
On a component mounting substrate that has been completed, however, most of the solder is overlapping with lands and components are over the solder. It is difficult to make judgments on the conditions of individual components by separating them from such superposed portions. Inspection apparatus using laminography have been proposed in view of this problem but they are not easy to introduce for actual use because their structure is complicated and the production cost is adversely affected.